Summary

The Cooperative Atmospheric Surface Exchange Study October 1999 (CASES-99) field observational program represents the second study to investigate linkages between the atmosphere and the Earth's surface. This study is designed to examine events in the nighttime boundary layer, and to investigate the physical processes associated with evening and morning transition regimes. The overall effort encompasses observation, data analyses and numerical modeling to achieve an understanding of episodic events that populate the nighttime stable boundary layer.

Objectives:

CASES-99 will combine measurements and data analyses with state-of-the-art numerical modeling to investigate the following areas of scientific interest: 1) Provide a time history of internal gravity waves, KH shear instabilities, and turbulence events in the nighttime stable boundary layer and evaluate the relative contributions to intermittent heat, moisture and momentum fluxes associated with these phenomena. 2) Measure heat and momentum fluxes and their divergence accompanying the events contributing to turbulence, transports, and mixing throughout the nocturnal boundary layer, and especially within the surface layer (~10-20 m) to assess the departures from similarity theory under weakly stable and very stable conditions. 3) Define the relative importance of surface heterogeneity, particularly under very stable light wind conditions, on the initiation of shallow drainage currents (O?10 m?) and the horizontal and vertical transports that accompany such boundary undulations. 4) Acquire data during the transition from a convective to a stable boundary layer regime and vice-versa to compare with existing models of this transition, and to assess the role of this transition period in the initiation of inertial oscillations and the enhancement of low-level jets ~ 100-300 m above the surface. rainfall estimation;evaluating dual-polarization rainfall estimation;determining length scales for soil moisture content.